DVB-S2标准更新：帧结构、编码与调制技术

DVB-S2

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"DVB-S2标准的最新更新，包括帧协议、调制和编码方式" DVB-S2（Digital Video Broadcasting - Satellite - Second Generation）是数字视频广播领域的一个重要标准，用于卫星广播、交互服务、新闻采集和其他宽带卫星应用。这个标准在DVB-S的基础上进行了改进，提升了效率和性能。描述中提到的"en_302307v010201p"可能是指该标准的某个具体修订版，即ETSI EN 302307 V1.2.1 (2009-08)，这是一份欧洲电信标准协会（ETSI）发布的技术规范。 DVB-S2的核心内容包括： 1. **帧协议结构**：DVB-S2采用了更高效的数据帧结构，包括前向纠错（Forward Error Correction, FEC）框架，使得数据传输更稳定且能抵抗信号干扰。帧通常由多个段组成，每个段包含不同数量的传输块，这些传输块通过交织和编码增强抗错误能力。 2. **调制方式**：DVB-S2支持多种高级调制方式，如QPSK（四相相移键控）、8PSK（八相相移键控）、16APSK（十六阶幅度相位键控）和32APSK（三十二阶幅度相位键控），这些调制方式允许根据信道条件动态调整，以最大化频谱效率。 3. **编码方式**：DVB-S2引入了低密度奇偶校验码（Low-Density Parity-Check, LDPC）和卷积码的组合，这种混合纠错编码系统提供了更高的错误纠正能力，特别是在噪声或干扰较大的卫星通信环境中。 4. **灵活的比特率和带宽适应**：DVB-S2标准允许服务提供商根据需要调整比特率和占用的卫星带宽，以满足不同服务质量（Quality of Service, QoS）的需求，例如高清电视传输或数据传输服务。 5. **预编码和多码率流**：DVB-S2支持预编码技术，可以优化多径衰落环境下的接收性能。同时，多码率流（Multiple Bit Rate, MBR）技术允许在同一频道内提供不同质量的服务，以适应不同接收设备的能力。 6. **兼容性和扩展性**：DVB-S2标准设计时考虑了与现有DVB-S系统的兼容性，同时也为未来的技术发展预留了空间，例如可能的增强或扩展特性。 DVB-S2标准的更新，如V1.2.1版本，通常会包含对原有标准的优化和修正，以应对技术进步带来的新需求和挑战。对于关心DVB-S2技术的人来说，查阅这样的更新文档可以帮助了解最新的技术进展和改进。有兴趣的用户可以通过ETSI官网获取该标准的电子版，或者从指定网络驱动器下载PDF参考版本。在存在争议的情况下，以ETSI内部打印的PDF版本为准。

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ETSI

ETSI EN 302 307 V1.2.1 (2009

08)

Forward Error Correction (FEC) Encoding shall be carried out by the concatenation of BCH outer codes and LDPC

(Low Density Parity Check) inner codes (rates 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 5/6, 8/9, 9/10). Depending on the

application area, the FEC coded block shall have length n

ldpc

= 64 800 bits or 16 200 bits. When VCM and ACM is

used, FEC and modulation mode may be changed in different frames, but remains constant within a frame. For

Backwards Compatible modes, the bit-stream at the output of the FEC encoder shall be processed according to annex F.

Bit interleaving shall be applied to FEC coded bits for 8PSK, 16APSK and 32APSK.

Mapping into QPSK, 8PSK, 16APSK and 32APSK constellations shall be applied, depending on the application area.

Gray mapping of constellations shall be used for QPSK and 8PSK.

Physical layer framing shall be applied, synchronous with the FEC frames, to provide Dummy PLFRAME insertion,

Physical Layer (PL) Signalling, pilot symbols insertion (optional) and Physical Layer Scrambling for energy dispersal.

Dummy PLFRAMEs are transmitted when no useful data is ready to be sent on the channel. The System provides a

regular physical layer framing structure, based on SLOTs of M = 90 modulated symbols, allowing reliable receiver

synchronization on the FEC block structure. A slot is devoted to physical layer signalling, including Start-of-Frame

delimitation and transmission mode definition. This mechanism is suitable also for VCM and ACM demodulator

setting. Carrier recovery in the receivers may be facilitated by the introduction of a regular raster of pilot symbols

(P = 36 pilot symbols every 16 SLOTs of 90 symbols), while a pilot-less transmission mode is also available, offering

an additional 2,4 % useful capacity.

Base-Band Filtering and Quadrature Modulation shall be applied, to shape the signal spectrum (squared-root raised

cosine, roll-off factors 0,35 or 0,25 or 0,20) and to generate the RF signal.

BBFRAME

FECFRAME

PLFRAME

FEC ENCODING

MODULATION

PL FRAMING

BCH

Encoder

bch

)

PL Signalling &

Pilot insertion

LDPC

Encoder

ldpc

)

BB Filter

and

Quadrature

Modulation

Bit

mapper

into

constel-

lations

QPSK,

8PSK,

16APSK,

32APSK

rates 1/4,1/3,2/5

1/2, 3/5, 2/3, 3/4, 4/5,

5/6, 8/9, 9/10

α=0,35, 0,25,

0,20

to the RF

satellite

channel

MAPPING

SCRAM

BLER

STREAM

ADAPTATION

PADDER

Signalling

Merger

Slicer

MODE ADAPTATION

SCRAM

BLER

Single

Input

Stream

Multiple

Input

Streams

BBHEADER

DATAFIELD

Bit

Inter-

leaver

Dummy

PLFRAME

Insertion

Null

packet

Deletion

(ACM, TS)

CRC

Encoder

Input Stream

Synchroniser

Input

interface

Null

packet

Deletion

(ACM, TS)

Input Stream

Synchroniser

Input

interface

DATA

ACM

COMMAND

Dotted sub-systems are

ot relevant for

single transport stream

broadcasting

applications

CRC

Encoder

LP stream for

BC modes

Buffer

Mode

Adaptation

Input

Interface

(optional)

Figure 1: Functional block diagram of the DVB-S2 System

4.3 System configurations

Table 1 associates the System configurations to the applications areas. According to table 1, at least "Normative"

subsystems and functionalities shall be implemented in the transmitting and receiving equipment to comply with the

present document Guidelines for mode selection are given in annex H.

ETSI

ETSI EN 302 307 V1.2.1 (2009

08)

Table 1: System configurations and application areas

System configurations

Broadcast

services

Interactive

services

DSNG

Professional

services

QPSK 1/4,1/3, 2/5

O N N N

1/2, 3/5, 2/3, 3/4, 4/5, 5/6,

8/9, 9/10

N N N N

8PSK 3/5, 2/3, 3/4, 5/6, 8/9, 9/10 N N N N

16APSK 2/3, 3/4, 4/5, 5/6, 8/9, 9/10 O N N N

32APSK 3/4, 4/5, 5/6, 8/9, 9/10 O N N N

CCM N N (see note 1) N N

VCM O O O O

ACM NA N (see note 2) O O

FECFRAME (normal) 64 800 (bits) N N N N

FECFRAME (short) 16 200 (bits) NA N O N

Single Transport Stream N N (see note 1) N N

Multiple Transport Streams

O O (see note 2) O O

Single Generic Stream NA O (see note 2) NA O

Multiple Generic Streams NA O (see note 2) NA O

Roll-off 0,35, 0,25 and 0,20 N N N N

Input Stream Synchronizer NA except

(see note 3)

O (see note 3) O (see note 3)

O (see note 3)

Null Packet Deletion NA except

(see note 3)

O (see note 3) O (see note 3)

O (see note 3)

Dummy Frame insertion NA except

(see note 3)

N N N

N = normative, O = optional, NA = not applicable.

NOTE 1: Interactive service receivers shall implement CCM and Single Transport Stream.

NOTE 2: Interactive Service Receivers shall implement ACM at least in one of the two options: Multiple Transport

Streams or Generic Stream (single/multiple input).

NOTE 3: Normative for single/multiple TS input stream(s) combined with ACM/VCM or for multiple TS input streams

combined with CCM.

Within the present document, a number of configurations and mechanisms are defined as "Optional". Configurations

and mechanisms explicitly indicated as "optional" within the present document, for a given application area, need not be

implemented in the equipment to comply with the present document. Nevertheless, when an "optional" mode or

mechanism is implemented, it shall comply with the specification as given in the present document.

5 Subsystems specification

The subsystem specification description is organized according to the functional block diagram of figure 1.

5.1 Mode adaptation

This sub-system shall perform Input Interfacing, Input Stream Synchronization (optional), Null-packet deletion (for TS

input streams and ACM only), CRC-8 encoding for error detection (for packetized input streams only), input stream

merging (for multiple input streams only) and input stream slicing in DATA FIELDs. Finally, base-band signalling

shall be inserted, to notify the receiver of the adopted Mode Adaptation format.

According to figure 3, the input sequence(s) is (are):

• Single or multiple Transport Streams (TS).

• Single or multiple Generic Streams (packetized or continuous).

The output sequence is a BBHEADER (80 bits) followed by a DATA FIELD.

5.1.1 Input interface

The System, as defined in the present document, shall be delimited by the interfaces given in table 2.

ETSI

ETSI EN 3

02 307 V1.2.1 (2009

08)

Table 2: System interfaces

Location

Interface

Interface type

Connection

Multiplicity

Transmit station Input MPEG [1, 4] Transport Stream

(see note 1)

from MPEG multiplexer Single or multiple

Transmit station Input (see

note 2)

Generic Stream From data sources Single or multiple

Transmit station Input (see

note 3)

ACM command From rate control unit Single

Transmit station Output 70/140 MHz IF, L-band IF,RF

(see note 4)

to RF devices Single or multiple

Transmit station Input Mode Adaptation from Mode Adaptation

block

Single

NOTE 1: For interoperability reasons, the Asynchronous Serial Interface (ASI) with 188 bytes format, data burst

mode (bytes regularly spread over time) is recommended.

NOTE 2: For data services.

NOTE 3: For ACM only. Allows external setting of the ACM transmission mode.

NOTE 4: IF shall be higher than twice the symbol rate.

The input interface subsystem shall map the input electrical format into internal logical-bit format. The first received bit

will be indicated as the Most Significant Bit (MSB).

A Transport Stream shall be characterized by User Packets (UP) of constant length UPL = 188 × 8 bits (one MPEG

packet), the first byte being a Sync-byte (47

HEX

A Generic Stream shall be characterized by a continuous bit-stream or a stream of constant-length User Packets (UP),

with length UPL bits (maximum UPL value 64 K, UPL = 0

means continuous stream, see clause 5.1.5). A variable

length packet stream, or a constant length packet exceeding 64 kbit, shall be treated as a continuous stream.

For Generic packetized streams, if a synch-byte is the first byte of the UP, it shall be left unchanged, otherwise a

sync-byte = 0

shall be inserted before each packet, and UPL shall be increased by eight. UPL information may be

derived by static modulator setting.

"ACM Command" signalling input shall allow setting, by an external "transmission mode control unit", of the

transmission parameters to be adopted by the DVB-S2 modulator, for a specific portion of input data. ACM command

shall be according to clause D.1.

Mode Adaptation (optional input) shall be a sequence of Data Fields (according to clause 5.1.5), where each individual

Data Field is preceded by a BBHEADER, according to clause 5.1.6 and to figure 3, and Stream Adaptation Command,

according to clause I.1, to allow setting, by an external 3mode adaptation unit", of the transmission parameters to be

adopted by the DVB-S2 modulator, for each specific MA Packet. Mode Adaptation shall be according to clause I.1

(separate signalling circuit) or I.2 (in-band signalling).

5.1.2 Input stream synchronizer (optional, not relevant for single TS - BS)

Data processing in the DVB-S2 modulator may produce variable transmission delay on the user information. The Input

Stream Synchronizer subsystem (optional) shall provide suitable means to guarantee Constant-Bit-Rate (CBR) and

constant end-to-end transmission delay for packetized input streams (e.g. for Transport Streams). This process shall

follow the specification given in annex D. Examples of receiver implementation are given in annex G.

5.1.3 Null-Packet Deletion (ACM and Transport Stream only)

For ACM modes and Transport Stream input data format, MPEG null-packets shall be identified (PID = 8191

) and

removed. This allows to reduce the information rate and increase the error protection in the modulator. The process is

carried-out in a way that the removed null-packets can be re-inserted in the receiver in the exact place where they

originally were. This process shall follow the specification given in annex D.

ETSI

ETSI EN 302 307 V1.2.1 (2009

08)

5.1.4 CRC-8 encoder (for packetized streams only)

If UPL = 0

(continuous generic stream) this sub-system shall pass forward the input stream without modifications.

If UPL ≠ 0

the input stream is a sequence of User Packets of length UPL bits, preceded by a sync-byte (the sync-byte

being = 0

when the original stream did not contain a sync-byte).

The useful part of the UP (excluding the sync-byte) shall be processed by a systematic 8-bit CRC encoder. The

generator polynomial shall be:

g(X) = (X

+1)(X

+X+1)(X+1) = X

The CRC encoder output shall be computed as:

CRC = remainder [X

u(X) : g(X)]

Where u(X) is the input sequence (UPL - 8 bits) to be systematically encoded. Figure 2 gives a possible implementation

of the CRC generator by means of a shift register.

The register shall be initialized to all zeros before the first bit of each sequence enters the circuit.

The computed CRC-8 shall replace the sync-byte of the following UP. As described in clause 5.1.6, the sync-byte is

copied into the SYNC field of the BBHEADER for transmission.

UP (excluding sync-byte)

Switches: in A for UPL

8 bits; in B for 8 bits

CRC-8

UPL

Compute

CRC-8

Replace

Sync-byte

=EXOR

Figure 2: Implementation of the CRC-8 encoder

5.1.5 Merger/Slicer

According to figure 3, the Merger/Slicer input stream(s) is (are) organized as Generic continuous Stream(s) or

Packetized Input Stream(s). The UP length is UPL bits (where UPL = 0 means continuous sequence). The input

stream(s) shall be buffered until the Merger/Slicer may read them.

The Slicer shall read (i.e. slice) from its input (single input stream), or from one of its inputs (multiple input streams) a

DATA FIELD, composed of DFL bits (Data Field Length), where:

bch

-(10x8) ≥ DFL ≥0 (K

bch

as per table 5, 80 bits are dedicated to the BBHEADER, see clause 5.1.6).

The Merger shall concatenate, in a single output, different data fields read and sliced from one of its inputs. In presence

of a single stream, only the slicing functionality applies.

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